Polyphenylene-oxide-organopolysiloxane block co-polymers

ABSTRACT

Block copolymers having polyphenylene oxide segments and polydimethylsiloxane segments, with the units present in critical length ratios, are useful as surface tension depressants for dielectric fluids, particularly dielectric fluids of the askarel type.

United States Patent Clark et al.

[54] POLYPHENYLENE-OXIDE- ORGANOPOLYSILOXANE BLOCK CO- POLYMERS lnventors: Robert F. Clark, Glendale Heights, 111.; Karl W. Krantz, Schenectady, NY.

Assignee: General Electric Company Filed: March 5, 1971 Appl. No.: 121,535

[52] US. Cl ..260/448.8 R, 252/63, 252/66,

252/351, 260/465 R [51] Int. Cl. ..C07f 7/18 [58] Field of Search ..260/448.8 R

[56] References Cited UNITED STATES PATENTS 2,386,793 10/1945 Hanford ..260/448.8RX

[151 3,696,137 1 Oct. 3, 1972 10/1959 Shibe ..260/448.8 R 3,125,635 3/1964 Murray et al....260/448.8 R X 3,270,133 8/1966 Holub ..260/448.8 R X 3,354,194 11/1967 Kaufman ..260/448.8 R

57] ABSTRACT Block copolymers having polyphenylene oxide segments and polydimethylsiloxane segments, with the' units present in critical length ratios, are useful as surface tension depressants for dielectric fluids, particularly dielectric fluids of the askarel type.

3 Claims, No Drawings POLYPHENYLENE-OXIDE I ORGANOPOLYSILOXANE BLOCK CO- A POLYMERS BACKGRCUND OF THE INVENTION Block copolymers of polycarbonates and polysiloxanes are known to lower the surface tension of dielectric fluids,-particularly chlorinated biphenyl capacitor fluids, such as Pyranol. Reduction of the surface tension of these dielectric fluids, so long as the surface tension depressant remains compatible, is of value in capacitor design. A prime function of such fluids is to displace all gas bubbles and fill all voids between the electrically conducting elements and the dielectric spacer(s), and also within the latter if initially of porous structure. A lowsurface tension enables the fluid to penetrate, purge all gas bubbles and wet all surfaces with maximum efiicie ncy. While, based upon chemical factors, it would appea that block copolymers-of polyphenylene oxide and polydimethylsiloxanesv would .be soluble in Pyranol dielectrics, so as to provide similar benefits, this is not the case.

SUMMARY OF THE INVENTION 7 In accordance with the present invention it was unexpectedly discovered that, while block copolymers of polyphenylene oxide and polydimethylsiloxanes would, indeed, reduce the surface tension of dielectric fluids, such as Pyranol, the polyphenylene oxidepolydimethylsiloxane block copolymers are soluble in the dielectric fluids only when the length of'the polyphenylene oxide segment and the length of the polydimethylsiloxane segment are closely controlled. In particular, if the lengths of the polyphenylene oxide segments separating the polydimethylsiloxane segments are too long or too short, or the length of the polydimethylsiloxane segments separating the polyphenylene oxide are too long or too'short, the material is not soluble in the dielectric fluid.

Use of polyphenylene oxide-organopolysiloxane block copolymers as surface tension depressants for iitifl H Li... J

i U K? J where Me ismethyl is phenyl, a is from 4 to 7, b is from to 500, the sum of x and y is from 2 to 17, n is from 2 to 10, and t is l or more DESCRIPTION OF THE PREFERRED EMBODIMENTS I segments, and for the length of the polyphenylene oxide segment separating the polydimethylsiloxane segments. In particular, there must be from four to seven dimethylsiloxane groups between each polyphenylene oxide segment in a recurring chain, and between five and 20 diphenylphenoxide groups between each polydimethylsiloxane segment.

As noted in the formula, additional polydimethylsiloxane blocks are permissible within thechain, but

only so long asa series of blocks with the critical lengths also exist. Thus, additional polydimethylsiloxane segments may be present, with b having a value of from 0 to 500, preferably from Qto 200.

There must be recurring polyphenylene oxide and polydimethylsiloxane segments of the critical size range within theblock copolymer, in addition to any further polydimethylsiloxane units which are present. Thus, n is from 2 to 10, preferably frorn .2 to 4. The intrinsic viscosity of the material is not critical and, thus, I is l or more. i v

The (BA), block copolymers employed in the present invention are formed by the method described in copending application Ser. No. 121,518, filed of even date herewith and assigned to the same assignee as the present invention. In the formula B is a polyphenylene oxide segment and A is a polydimethylsiloxane segment. The polyphenylene oxide segments are incorporated into the block copolymer employing, as a reactant, the difunctionally terminated polyphenylene oxide oligomers described and claimed in the copending application of Karl W. Krantz, Ser. No. 121,517, filed of even date herewith and assigned to the same assignee as the present invention.

As described in the first-mentioned copending application, the block copolymers are formed by the rea'c- 'tion of the difunctionally terminated polyphenylene into the block copolymer employed according to the present invention by the back coupling reaction, also described and claimed in the first-mentioned copending application.

3 4 EXAMPLE 1 lar block copolymers to be employed according to the In accordance with the present invention, a block present invention, a block copolymer of the structure copolymer of polyphenylene oxide and polydimethyl- ABA having the formula:

l l Fri l l l JL JL J 45 is 188 I 176 p 188 siloxane was prepared having the structure of formula] where Me is methyl and (b is phenyl, was prepared. where a was 7, b was 92, the sum of x and y was 6.3, n The material had an intrinsic viscosity, in methylene was 4, and t was greater than I. This block copolymer chloride at 25C, of 0.67 dl'./g. and a polyphenylene had an intrinsic viscosity, in toluene at 25 C, of 0.5 oxide content of 88.weight percent. Based upon the indl./g. and a polyphenylene oxide content of 49 weight trinsic viscosity, the organic character of the polymer, percent. The material was completely soluble in and the great separation of the polyphenylene oxide Pyranol and acted as asurface tension depressant. Segments, it would be predicted that 1 this material EXAMPLE 2 would act as a surface tension depressant. However,

Y the material was insoluble in Pyranol, thus establishing A block copolymer of p yp y Oxide and the criticality. of the polyphenylene oxide block length. Polydimethylsiloxane was P p in accordance with Pyranol is a trademark for dielectric materials, prinformula 1 Where a as b Was the Sum Ofx and y cipally of the askarel type. The askarel type of dielecwas 6.3, n was 4, and t was greater than 1. The intrinsic trics are synthetic, non-flammable, electrical insulating viscosity of this material, in toluene at C, was 0.91 materials which evolve only non-explosive gases or dlJg. This material acted as a surface tension depresg OuS xture-8' On deCOmPOSitiOn by an electric arc. sant for Pyranol, but was marginally soluble in the Particular examples of such materials are chlorinated P r noL 25 aromatic derivatives, particularly pentachlorodiphenyl and trichlorobenzene. Smaller amounts of en- EXAMPLE 3 tachlorodiphenyl oxide, pentachlorophenylbenz ate, A block copolymer of polyphenylene. oxide and e 'o p ny ethane, PentaChlorOdiphenylpolydimethylsiloxane was prepared where the material ketone, and pentachlomethylbenzene y also be had the structure of formula I where a was 1, b was 92, the sum of x and y was 6.3 n was 4 and t was greater In accordance with the present invention, the utility than 1. This material had an intrinsic viscosity, in of pamcular polyphenylene oxldepolydlmethylsllox' toluene at C of 072 d1 Though having a lower ane block copolymers as surface tension depressants intrinsic viscosity than the material'of example 2, the for askarel type .dlelecmc flulds has been demon block copolymer of this example was insoluble in 'f The l l l examples Shown Should not be Pyranol and thus could not act as a surface tension considered as hmmng the scope and coverage of the depressant This is contrary to expectation Since at present invention,asmore particularly described in the d d l identical polyphenylene oxide block length and nearly ap ciai13 identical polyphenylene content, it would be expected 40 l. A surface tension depressant for chlorinated arothat solubility would be based upon the intrinsic matic dielectric fluids having the formula:

rr iil L l, LT@I1 I i f llif ll g-la n viscosity. Thus, in combination with the marginal solua is from 4 to 7, b is from 0 to 500, the sum of x bility of the block copolymer of example 2, thisexamand y is from 2 to 17, n is from I to 4, and t is 1 or more. ple establishes the criticality of length of the 2. The surface tension depressant of claim 1 wherein polydirnethylsiloxane segments. n is from 2 to 4.

. 3. The surface tension depressant of claim 1 wherein EXAMPLE 4 b is from 0 to 200.

To further demonstrate the criticality of the particu- 

2. The surface tension depressant of claim 1 wherein n is from 2 to
 4. 3. The surface tension depressant of claim 1 wherein b is from 0 to
 200. 